Evaluation of MRI T1-based treatment monitoring during laser-induced thermotherapy of liver metastases for necrotic size prediction

Figures & data

Figure 1. (A) T1-weighted gradient echo (GRE) sequence in the coronal plane to verify sheath position after CT-guided insertion of laser fibres before LITT procedure (FLASH, TE/TR 4.8/119, FA 90°, TA 2 s). Magnetic artefacts are caused by a magnetic marker inside the applicator system to enable a sufficient verification of the position. (B) MRI obtained after removal of the magnetic markers demonstrates the hypointense metastasis from a sarcoma in segment 4b with two laser fibres inserted.

Figure 2. Display of progress of LITT treatment in a 69-year-old patient with liver metastasis from colorectal cancer in segment 8. (A) The T1-weighted axial GRE sequence (FLASH, TE/TR 4.8/119, FA 90°, TA 2 s) shows the metastasis (arrow) before LITT after removal of the magnetic marker between the laser fibres. (B) T1-weighted GRE sequence (same settings) shows the laser fibres 2 min after the start of the LITT procedure. An ellipsoidal-shaped area of hypointensity can be demarcated according to thermal damage. (C) MRI obtained with the same settings after 4 min of ablation. The area of coagulation is enlarging. (D) Image obtained after 9 min: necrosis manifests and an area with a total signal loss can be demarcated.

Figure 3. Mean energy amount (kJ) applied according to the treated metastasis diameter.

Figure 4. Mean values of the applied energy/volume (kJ/cm³) according to the segmental distribution of liver metastases treated with LITT.

Table I. Amount of energy applied per volume of treated metastases during LITT.

Liver segment	n	Mean (kJ/cm^3)	Minimum (kJ/cm^3)	Maximum (kJ/cm^3)	SD (kJ/cm^3)
1	1	1.31	1.31	1.31	–
2	23	1.93	0.34	5.48	1.17
3	23	1.52	0.26	4.60	1.12
4	43	1.94	0.40	6.91	1.53
5	31	2.12	0.40	5.73	1.30
6	19	1.61	0.57	4.87	1.12
7	56	1.52	0.28	4.53	0.85
8	40	2.16	0.59	9.60	1.55

Figure 5. Comparison between the last MRI T1-based treatment monitoring image, contrast-enhanced MRI obtained immediately after LITT and the contrast-enhanced MRI obtained 24 h after the treatment. (A–C) A 57-year-old patient with a hepatic metastasis in segment 4b. (D–F) Liver metastasis from colorectal cancer in segment 8 from a 69-year-old patient. (A) and (D) T1 weighted GRE sequences (FLASH, TE/TR 4.8/119, FA 90°, TA 2 s) demonstrate imaging of the progress of LITT treatment just before the end of the ablation procedure. Although image A is affected by motion of the surrounding organs, signal loss can clearly be demarcated due to the thermally induced cell damage. (B) and (E) T1 weighted contrast-enhanced GRE sequences after LITT (FLASH, TE/TR 4.8/119, FA 90°, TA 2 s) depict an area of enlarging hypointensity; a slight benign peripheral enhancement according to the reactive tissue reaction can also be demarcated [10]. (C) and (F) Contrast-enhanced T1 weighted GRE (FLASH, TE/TR 101/1000 ms, FA 150°, TA 1 s/slice) show an extended hyperintense coagulation zone. In both cases a reposition of the applicator was performed to maximise the ablation zone. (C) depicts a larger coagulation area due to the two laser fibres used during the treatment, whereas (F) shows a rather ellipsoid shaped area. The puncture track is still visible as a thin dark hypointensity within the necrotic area.

Table II. Mean energy applied and resulting volumes (mean) compared to the metastatic diameter prior to LITT treatment.

Diameter (cm)	n	Energy (kJ)	Volume 1^a (cm^3)	Volume 2^b (cm^3)	Volume 3^c (cm^3)	Volume 4^d (cm^3)
<=2	137	34.68	0.60	19.37	10.93	21.52
2–3	60	61.20	5.05	31.22	19.09	32.92
3–4	24	80.22	15.71	53.56	35.02	63.07
>4	16	85.68	31.02	75.26	49.70	79.16

^aVolume prior to LITT.

^bVolume for the last available T1 treatment monitoring image.

^cVolume for contrast-enhanced MRI directly after LITT.

^dVolume 24 h after LITT.

Table III. Mean measured volumes of ablated metastases during follow-up MRI.

Diameter (cm)	Volume 1^a (cm^3)	Volume 2^b (cm^3)	Volume 3^c (cm^3)	Volume 4^d (cm^3)
<=2	21.52	11.34	6.83	5.80
2–3	32.92	18.16	12.47	8.06
3–4	63.07	33.46	30.39	32.42
>4	79.16	37.84	24.38	8.22

^aVolume 24 h after LITT.

^bVolume after 3 months.

^cVolume after 6 months.

^dVolume after 12 months.

Figure 6. Correlation of necrosis volume measured 24 h after LITT with volume measured on contrast-enhanced MRI immediately after LITT (a), and MRI T1-based treatment monitoring during the ablation procedure (b). Z -standardisation demonstrates a narrowed scatter range of values on correlation of MRI T1-based treatment monitoring with MRI 24 h after LITT (b).

Goldberg SN, Grassi CJ, Cardella JF, Charboneau JW, Dodd GD, Dupuy DE, et al. Image-guided tumor ablation: Standardization of terminology and reporting criteria. J Vasc Interv Radiol 2009;20:377–90

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